Tool for implantable neural electrode

ABSTRACT

An implantable electrode system for establishing electrical contact with nerve tissue. The outer substrate of the electrode is a semi-rigid, body compatible, insulating material such as a chronically implantable polymer. The outer substrate is molded as a single structure having a central spine along the longitudinal axis of the electrode. A plurality of fingers extend orthogonally from the central spine, and are bent circularly about a radius of curvature approximating that of the nerve to be contacted. The fingers of the electrode are spread by the retractable channel of the insertion tool during the implant procedure. The retractable channel is placed over the selected nerve and a retraction knob on the handle of the insertion tool is moved in a proximal direction causing the electrode to be ejected on to the nerve. The handle of the insertion tool is curved to require a minimum of exposure of the nerve tissue.

CROSS REFERENCE OF CO-PENDING APPLICATIONS

This application is related to Ser. No. 07/446,865, filed Dec. 6, 1989,now U.S. Pat. No. 5,031,621, entitled "Nerve Electrode with BiologicalSubstrate"; Ser. 07/483,455, filed Feb. 22, 1990, now U.S. Pat. No.5,082,332, entitled "Steroid Eluting Cuff Electrode for Peripheral NerveStimulation"; and Ser. No. 07/536,286, now U.S. Pat. No. 5,095,905,filed Jun. 7, 1990, entitled "Implantable Neural Electrode", all ofwhich are assigned to the assignee of this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to implantable medical devices,and more particularly, relates to implanting electrodes for electricallycoupling to nerve tissue.

2. Description of the Prior Art

The use of electrodes to monitor electrical activity and stimulate bodytissue is quite old. U.S. Pat. No. 1,662,446 issued to R. H. Wapplerteaches an early electrode system. The Wappler electrode is used foracute stimulation only, and is not implantable.

An early stimulation electrode which is chronically implantable istaught by S. I. Schwartz, et al. in U.S. Pat. No. 3,421,511, hereinincorporated by reference. U.S. Pat. No. 3,654,933 issued to Hagfors,herein incorporated by reference, teaches an improved stimulationelectrode for chronic implantation. Clinical experience with theelectrodes taught by Schwartz et al. and Hagfors has shown a potentialfor excess irritation in certain applications. This irritation resultsin swelling of the nerve tissue which is exacerbated by the fixeddiameter of the cuff of each device after being sutured into place.

U.S. Pat. No. 3,738,368 issued to Avery, et al., U.S. Pat. No. 3,774,618issued to Avery, and U.S. Pat. No. 3,955,560 issued to Stein, et al. allteach electrodes having fixed diameters after chronic implantation.These electrodes also tend to cover relatively large areas of the nervetissue, thus depriving nutrient access to great numbers of adjacentnerve cells.

U.S. Pat. No. 4,573,481 issued to Bullara suggests a neural electrodearray having a serpentine shape. This shape provides significant accessto nutrients by the nerve. This structure, however, provides difficultyin implantation. Because an increase in diameter of the electrode systemrequires a decrease in length, it is anticipated that the Bullaraelectrode system does not provide a satisfactory solution to the problemof nerve swelling.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of prior art neuralelectrodes by providing an electrode system which permits ease ofchronic implantation. This procedure produces a minimum of nerve tissueirritation. The desired result is provided by an electrode structuremolded of a semirigid polymer having a central spine with a plurality oforthogonal curved fingers. The fingers are not attached to one anotherto permit the diameter to vary. Enhanced nutrient access is provided bythe large open surface area. The implant procedure is easilyaccomplished by spreading the fingers with a tool and sliding the outersubstrate over the nerve tissue.

The inner surface of the fingers is provided with a conducting foil.This foil is coupled proximal to the electrode by conductors positionedalong the central spine.

The implantation procedure is accomplished using an implantation toolhaving a proximal handle and a movable distal channel. The distalchannel has a radius of curvature significantly greater than the radiusof curvature of the nerve tissue. Mounting the electrode structure onthe outer surface of the distal channel causes spreading of the fingersto permit the combination to be easily slipped over the nerve. Curvatureof the distal channel enables implantation with a minimum of exposure ofthe nerve tissue.

The combination is placed over the nerve tissue. A sliding knob locatedin the proximal handle and coupled to the distal channel is pulledproximally while the electrode structure is held by the electrode stopcausing it to be slid from the distal end of the distal channel. Thememory of the semi-rigid fingers tends to keep the electrode system inplace along the selected nerve.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects of the present invention and many of the attendantadvantages of the present invention will be readily appreciated as thesame becomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, in which like reference numerals designate like partsthroughout the figures thereof and wherein:

FIG. 1 is a perspective view of the structure of a neural electrodeusing in the present invention;

FIG. 2 is a top view of the preferred mode of the neural electrode;

FIG. 3 is a bottom view of a preferred embodiment of the neuralelectrode;

FIG. 3A is a bottom view of an alternate embodiment of the neuralelectrode;

FIG. 4 is a side view of the neural electrode mounted on theimplantation tool;

FIG. $ is a top perspective view of the implantation tool; and,

FIG. 6 is a side view of the implantation of the electrode system usingthe implantation tool.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a perspective view of a neural conductor or electrode used inthe present invention. The outer substrate or insulating structure ismolded of a semirigid biocompatible polymer material. It has alongitudinal element or central spine 12 which is along the longitudinalaxis of the electrode. Fingers 14a-14n extend from central spine 12, andcurve in a first direction as shown. Similarly, circumferential elementsor fingers 16a-16n extend and bend in the opposite direction. Centralspine 12, along with fingers 14a-14n and fingers 16a-16n, are molded asa single piece.

The radius of curvature of fingers 14a-14n and fingers 16a-16n areestablished to snugly, but not too tightly, fit around the nerve toreceive the implant. Because the fingers are molded of a semi-rigidpolymer, they can be spread to permit implantation over the nerve andreturn to the original shape for chronic use. The fingers are staggeredand not connected at the ends as is described in further detail below.

Electrical contact is established using a strip of conducting materialplaced inside one or more fingers. In this embodiment, electrode elementor metallic foil 18a is used on the inner surface of finger 14a, forexample. Metallic foil 18a is electrically coupled to the proximal endof electrode 10 (and hence an electronic circuit not shown) usingconductor 22a. In the preferred mode electrode lead-in or conductor 22ais vacuum deposited on the inner surface of central spine 12 as shown inthe phantom view.

Also in the preferred embodiment, fingers 14b-14n contain metallic foils1Bb-18n coupled to conductors 22b-22n. Similarly, metallic foils 20a-20nare positioned on the inner surfaces of fingers 16a-16n and coupled toconductors 24a-24n, respectively. Having electrically isolated metallicfoils permits the pulse generator electronic circuitry to providestimulation according to a large number of varying patterns.Alternatively, one or more of the metallic foils may be electricallycommon to one another rather than electrically isolated.

FIG. 2 is a top view of the outer substrate of electrode 10. Fingers14a-14n are attached orthogonal to central spine 12, and curve under asshown. The length of fingers 14a-14n is chosen to extend about one-halfway around the nerve to receive the implant. As can be seen distal tips26a-26n represent the free ends of fingers 14a-14n, respectively.

Fingers 16a-16n are of equivalent length to fingers 14a-14n, and extendfrom central spine 12 in the opposite direction as shown. In thepreferred embodiment, fingers 14a-14n are staggered from fingers 16a-16nas shown. Fingers 16a-16n terminate in distal tips 28a-28n,respectively. The spacing between fingers may be varied to accommodatethe different applications.

FIG. 3 is a bottom view of the preferred embodiment. All components areas previously described.

FIG. 3A is a bottom view of an alternative embodiment of electrode 11.In this mode fingers 15a-15n are not staggered from fingers 17a-17n inattachment to central spine 13. This differs from the preferred mode inthat spreading of the fingers results in no overlap at all, andtherefore greater nerve surface area for nutrient access.

FIG. 4 is a side view of implantation tool 30. It has a handle 40 (onlypartially shown) which is held by the implanting physician. Handle 40 ishollow to accommodate flexible distal channel 32, which is a channelopening downward. The lateral radius of curvature of distal channel 3must be greater than the diameter of the nerve to receive the implant.Similarly, the opening at the bottom of distal channel 32 must be widerthan the diameter of the nerve to receive the implant (see also Fib. 5).The portion of distal channel 32 which is distal to handle 40 must be atleast as long as electrode 10 such that electrode 10, with its fingersspread, fits completely over distal channel 32.

During implantation, it is desirable to expose only the minimum amountof nerve surface. To assist in implantation, distal channel 32 curves atbend 34. This permits distal channel 32 to be withdrawn away from theimplant site.

Retracting knob 36 is attached to the proximal end of distal channel 32as is shown in phantom. Because of slot 35 in handle 40 (see also FIG.5), retracting knob 36 is free to move in the direction of arrow 37.Retracting knob 36 is shown in its most distal position.

FIG. 5 is an perspective end view of implantation tool 30 disposed overnerve 50. Note that distal channel 32 conveniently slides over nerve 50.Electrode 10 has its fingers spread to enable it to be positioned on theouter surface of distal channel 32.

FIG. 6 shows electrode 10 as partially implanted aruond nerve 50 usingimplantation tool 30. The implantation is completed as distal channel 32is slowly (shown in phantom) retracted into handle 40 by proximal motionof retracting knob 36 and electrode 10 is held in a fixed position withrespect to nerve 50. As fingers 14a-14n (and fingers 16a-16n, not shown)are slid from the distal end of distal channel 32, they tend to resumetheir original cylindrical shape about nerve 50. The diameter of theresulting cylinder may be chosen at manufacture to fit loosely or snuglyabout nerve 50 as medical requirements might dictate.

Having thus described the preferred embodiments of the presentinvention, those of skill in the art will be able to apply the teachingsfound herein to other embodiments without deviating from the scope ofthe claims hereto attached.

I claim:
 1. An electrode system for implanting a nerve tissue having anoutside diameter comprising:a. an implantable electrode having agenerally cylindrical body with a plurality of flexiblecircumferentially directed elements and having an electricallyconductive surface; b. a channel having an interior size greater thansaid outside diameter of said nerve tissue whereby said plurality offlexible circumferentially directed elements may be spread to positionsaid implantable electrode on said channel and having said implantableelectrode positioned thereon; and c. means coupled to said channel forejecting said implantable electrode from said channel.
 2. An electrodesystem according to claim 1 further comprising a handle attached to saidchannel and said ejecting means.
 3. An electrode system according toclaim 2 wherein said channel is retractably inserted within said handle.4. An electrode system according to claim 3 wherein said ejecting meansis slidably mounted on said handle.